Transmission belts comprising a cord with at least two fused yarns

ABSTRACT

A transmission belt is made of a cord, a rubber or thermoplastic matrix, and an adhesion material which is able to adhere the cord to the rubber or thermoplastic matrix. The cord is made of at least two yarns, such that a first yarn has a melting or decomposition point T 1  and a second yarn has a melting point T 2 , wherein T 1 &gt;T 2 . A ratio of a linear density of the first yarn to a linear density of the second yarn is between 1,000:1 and 1:1, wherein the second yarn is fused to the first yarn. A method of making such cords includes intertwining the first and the second yarn and then heating to a temperature between T 1  and T 2 , with the heating step being integrated with or followed by a step wherein the cord is subjected to a dipping treatment with a rubber adhesion material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a transmission belt comprising a cord with atleast two fused yarns, to a method of manufacturing the cord, and to amethod of manufacturing the transmission belt.

2. Discussion of Related Art

Cords for reinforcing rubber articles are known in the art. A cord forthat purpose comprising at least one high-modulus yarn and at least onelow-modulus yarn is disclosed in WO 97/06297. The yarns of these cordsmay be twisted together and can be dipped with a rubber adhesivematerial. The low-modulus yarn is primarily added as a process aid toenable high-modulus yarns to be used in mould curing processes. By thismethod transmission belts can be produced; however, during theprocessing of such belts the mechanical properties of the cord tend todeteriorate.

High bundle cohesion is essential to avoid fraying when the belts gettheir final shape as they are cut out of a rubber composite slab. Inorder to produce a clean cut, all the filaments in the yam bundle haveto be secured firmly together in the cutting plane. If they are not heldin place, the applied cutting force can move filaments out of thecutting plane, causing filaments to be cut at different lengths (theeffect called “fraying”). In order to meet the quality standards set bythe belt industry, fraying must be kept to an absolute minimum, not foroptical reasons only but also to prevent a possible failure initiation.For that reason both aramid and polyester cords are usually pre-dippedwith a solvent-based MDI (diphenylmethane-4,4-diisocyanate) pre-dip toobtain high filament coherence. The pre-dipping with MDI results in arather stiff cord with excellent cutting behavior, though at the cost ofpoor strength efficiency after the dipping process (10 to 20% strengthloss compared to standard “soft-dipping”). Moreover, it was found thatstiff-dipped p-aramid cords suffer from severe strength loss afterhandling and vulcanization. This strength loss is proportional to thestiffness (i.e. the degree of impregnation) and is presumably induced bykink bands while buckling the stiff aramid cords. This phenomenonresulting in loss of strength while handling or processing stiff-dippedcords is called “handling resistance” or “handleability”.

SUMMARY OF THE INVENTION

It is an object of the present invention to manufacture transmissionbelt using cords with high bundle cohesion, having high strengthefficiency and good adhesion while maintaining good handling resistance.This is particularly important for good cuttability behavior whileproducing open edge transmission belts.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will become apparent as thefollowing description proceeds and upon reference to the drawings, inwhich:

FIG. 1 is a schematic representation of a basic two-step twistingscheme.

FIG. 2 is a schematic representation of a basic three-step twistingscheme.

FIG. 3 is a schematic representation of a preferred method of twisting atypical construction for a transmission belt application and of thethree-step twisting scheme of Example 4F.

FIG. 4 is a schematic representation of a Litzler laboratory dippingunit.

FIG. 5 is a schematic representation of a two-step twisting scheme ofExample 3A.

FIG. 6 is a schematic representation of a two-step twisting scheme ofExample 3B.

FIG. 7 is a schematic representation of a two-step twisting scheme ofExample 3C.

FIG. 8 is a schematic representation of a three-step twisting scheme ofExample 4D.

FIG. 9 is a schematic representation of a three-step twisting scheme ofExample 4E.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention pertains to a transmission belt comprising a cord, arubber or thermoplastic matrix, and an adhesion material which is ableto adhere the cord to the rubber or thermoplastic matrix, wherein thecord is made up at least two yarns, the first being a yarn with amelting or decomposition point T₁, and the second being a yarn with amelting point T₂, wherein T₁>T₂ and the ratio of the linear density ofthe first yarn to the linear density of the second yarn is between1,000:1 and 1:1, wherein the second yarn is fused to the first yarn.

Preferably, the ratio of the linear density of the first yarn to thelinear density of the second yarn is between 100:1 and 4:1, and morepreferably between 35:1 and 15:1.

For use in transmission belts the cord of the instant invention mustcontain a rubber or thermoplastic matrix adhesion material. Examples arechloroprene rubber (CR), hydrogenated butadiene acrylonitrile rubber(HNBR), alkylated chlorosulfonated polyethylene (ACSM), ethylenepropylenediene rubber (EPDM), polyurethane (PU).

In order to ensure that in the transmission belt there is good adhesionof the cords to the matrix material of the belt, it is required to coatthe cords with an adhesive. Therefore, the cords are treated with anadhesive system prior to being contacted with the matrix material.Preferably, the cords are provided with a first adhesive coating beforethey are treated with the rubber or the thermoplastic matrix adhesivematerial.

Highly suitable first adhesive coatings include epoxy compounds,polymeric methyl diphenyl diisocyanate (e.g., VORANATE® ex DOW), andpolyurethanes having ionic groups.

The adhesive system also offers several options. Highly suitable for usein the case of, e.g., poly(para-phenylene terephthalamide) are aresorcinol/formaldehyde/latex (RFL) system and CHEMOSIL® (ex Henkel). Inthe case of, e.g., glass, use may be made of a silane compound.

The cord is particularly suitable for use in open-edge transmissionbelts, yet if the rubber adhesion treatment is omitted, the obtainedcord is also suitable for use in other applications where high bundlecohesion is desired, such as in ropes, cables, hoses, and the like.

Highly suitable materials for yams with relatively high melting ordecomposition points (T₁) include aromatic polyamides (aramid), such aspoly(para-phenylene terephthalamide). Over the years these materialshave proved especially suitable for use in composites. Aramid isfrequently employed in composites with a rubber matrix among others.Other examples of appropriate materials are polyesters.

As suitable materials for yarns with relatively low melting points (T₂)may be mentioned polyesters, polyamides, polyolefins, elastodienes,elastanes, thermoplastic vulcanizates, and chlorofibres.

Some of these materials have been used in composites such as tires anddrive belts for many years. Other examples of suitable materials arepolyolefins, cellulose, acetate, acrylic material, and vinylal. Thepreferred yarn for transmission belt application is Perlon yarn 13—96dtex (PA6 POY, melting point ±220° C.).

The method of manufacturing the cord of this invention comprises thesteps of intertwining the first and the second yarn and then heating theintertwined cord at a temperature between T₁ and T₂, wherein the heatingstep is integrated with or followed by a step wherein the cord issubjected to a dipping treatment with a rubber adhesion material.

The heating step is performed to fixate the first yarn bundles bymelting the second (fusion) yarn. The molten filaments embrace thesingle plies, thereby interlocking the filaments and holding them inplace to enhance their cuttability.

The dipping treatment in order to prepare the cord for good adhesion torubber or thermoplastic matrix is a well-known process. Depending on thebasic cord yarn, a single- or two-bath dipping process can be used.

For technical and economical reasons, the fixation (heating) stepideally takes place during the dipping process. By selecting athermoplastic adhesive with a melting point within the range oftemperatures used for the dipping treatment, the heat setting can becombined with the dip-curing steps. By selecting a thermoplasticadhesive with a melting point between 200-250° C., the heat-setting canbe combined with the curing step in a conventional dipping process.Integrated RFL dipping and heat setting is the preferred method for theproduction of aramid cords for transmission belts.

The method can be applied to any cord construction; however, typicalapplications are cord constructions with a linear density ranging from210 to 50,000 dtex. A typical construction for transmission beltapplication is TWARON® 2300 1680 dtex×2 Z190×3 S115 (linear density:1680×2×3=10080 dtex).

The distribution of the second (fusion) yarn is controlled byintertwining the fusion yarn according to appropriate twisting schemesand is dependent on the type of cord construction. The twisting schemeand the amount of fusion yarn relative to the first yarn used depend onthe desired bundle cohesion and are easily determined by those skilledin the art. Twisting regimens are well-known in the art. The twistingcan be carried out with any suitable twisting equipment.

In order to distribute the adhesive for this cord, one can apply severaltwisting schemes, depending on the complexity of the cord construction.For TWARON® 2300 1680 dtex×2 Z190×3 S115 construction, for instance, abasic two-step twisting a scheme I or a basic three-step scheme II canbe used. The distribution of adhesive is controlled by varying thenumber of feed points and the positions where the fusion yarn is fedinto the aramid construction. When using a two-step basic twistingscheme, there are 6 feeding positions, with 12 different twisting schemepossibilities in total. See FIG. 1. If a three-step basic twistingpositions scheme is used, there are 12 feeding positions, with 72different twisting scheme possibilities in total. See FIG. 2.

The preferred method of twisting a typical construction for transmissionbelt application is shown in FIG. 3.

The invention is further illustrated by the following examples.

EXAMPLE 1

Dipping Conditions

For a typical aramid construction for transmission belt application thefollowing dipping conditions are chosen.

Two-bath procedure: Pre dipping conditions. dip: T03 (2%) GE100 epoxideoven 1 residence time: 120 sec temperature: 150° C. tension: 25 N RFLdipping conditions dip: VP latex A11 (25%) oven 2 residence time: 120sec temperature: 150° C. tension: 25 N oven 3 residence time:  60 sectemperature: 235° C. tension: 25 N One-bath procedure: RFL dippingconditions dip: VP latex A11 (25%) oven 1 residence time: 120 sectemperature: 150° C. tension: 25 N oven 2 residence time:  60 sectemperature: 235° C. tension: 25 N

The dip treatment was carried out on a Lizler laboratory dipping unitaccording to the known art of the two-bath-three-oven dipping procedureas shown in FIG. 4. The greige cord was reeled off at position a. TheGE-100 pre-dip was applied by submerging the cord in a dip container atposition c and subsequently curing it in oven 1. The RFL dip was applieda position g and was subsequently dried and cured in oven 2 and oven 3,respectively. At position h, the dipped cord was wound on a spool. Thedipping speed and the tension were maintained at a constant level by thecontrol units c, d, f, and g.

Preparation of T03 (2%) GE100 epoxide

To 978.2 g of demin (demineralized) water in a polyethylene bottle, 0.5g of piperazine was added, and the mixture was stirred with a glass roduntil the solids were dissolved. Under stirring with the glass rod, 1.3g of AEROSOL™ OT 75% (surfactant dioctyl sodium sulfosuccinate in 6%ethanol and 19% water) (Chemical Corporation Pittsburgh, Pa., USA) wereadded, and thereafter 20.0 g of GE-100 epoxide (mixture of di- andtrifunctional epoxide on the basis of glycidyl glycerin ether (RaschigAG, Ludwigshafen, Germany) were added. The mixture was stirredmechanically during 1 min and the preparation was matured for 12 h atroom temperature.

The storage life of this dip was five days in a refrigerator between5-10° C.

Formulation RFL Dip A11

Preparation:

A mixture of 275.3 g of demin water, 12.9 g of ammoniumhydroxide 25%,and 69.4 g of PENACOLITER® R50 50% (recorcinol-formaldehyde polymerresin solution) (Chemical Corporation Pittsburgh, Pa. USA) was added toPLIOCORD® VP106 (aqueous dispersion of a vinylpyridene-styrene-butadieneterpolymer (40%)) (Goodyear Chemicals, Europe, Les Ulis, France) andstirred during 3 min. A mixture of 23.1 g of formaldehyde 37% and 110.6g of demin water was added and stirred for another 3 min. The dip wasmatured for 12 h at room temperature.

The storage life of this dip is five days in a refrigerator between5-10° C.

EXAMPLE 2

The properties of the cords were measured as specified in documentIN97/7180, “Standard methods of testing Twaron filament yarns andcords”, version 4, 01-01-1997 of Twaron Products. For tensile testmethods reference is made to ASTM D885—“Standard Test Methods for Tirecords, Tire Cord Fabrics, and Industrial Filament Yarns” —and EN12562—“Para-aramid multi filament yarns—Test methods”.

The mechanical properties are listed in Table 1, comparing:severaldip-treated aramid cords samples.

Stiff Dipped:

-   a) MDI (2.5%)/A11 (20%): aramid cord dip-treated with    pre-dip-containing 2.5% MDI and RFL dip-treatment A11 (20%).-   b) MDI (5%)/A11 (20%): aramid cord dip-treated with    pre-dip-containing 5% MDI and RFL dip-treatment A11 (20%).-   c) MDI (10%)/A11 (20%): aramid cord dip-treated with    pre-dip-containing 10% MDI and RFL dip-treatment A11 (20%).    Soft Dipped:-   d) T03 (0.5%)/A11 (25%): newly developed aramid cord with    thermoplastic impregnation treated with pre-dip-containing 0.5%    GE100 epoxide and RFL dip-treatment A11 (25%).-   e) T03 (0.5%)/A11 (25%): aramid cord dip-treated with    pre-dip-containing 0.5% GE100 epoxide and RFL dip-treatment A11    (25%).-   f) T03 (1 %)/A11 (25%): newly developed aramid cord with    thermoplastic impregnation treated with pre-dip-containing 1 % GE100    epoxide and RFL dip-treatment A11 (25%).-   g) T03 (1 %)/A11 (25%): aramid cord dip-treated with    pre-dip-containing 1 % GE100 epoxide and RFL dip-treatment A11    (25%).-   h) T03 (2%)/A11 (25%): newly developed aramid cord with    thermoplastic impregnation treated with pre-dip-containing 2% GE100    epoxide and RFL dip-treatment A11 (25%).-   i) T03 (2%)/A11 (25%): aramid cord dip-treated with    pre-dip-containing 2% GE100 epoxide and RFL dip-treatment A11 (25%).

The following properties were measured according to internal procedures.

Dip Eff.-Absolute

dip efficiency absolute=percentage retained strength of cord after diptreatment relative to the absolute breaking strength of the untreatedgreige cord.Calculation:$\frac{{Absolute}\quad{breaking}\quad{strength}\quad{dipped}\quad{{cord}(N)}}{{Absolute}\quad{breaking}\quad{strength}\quad{greige}\quad{{cord}(N)}} \times 100\quad(\%)$Strap Peel Force

Adhesion test according ASTM D4393 using

-   a) CR compound=chloroprene rubber compound and-   b) NR compound=natural rubber compound Dunlop 5320.    Handle Ret. Strength

Handleability retained strength=absolute retained strength aftervulcanization and manual handling.

Handleability retained strength is measured after cords are extractedfrom a vulcanized rubber composite. Since this procedure not onlyincludes a vulcanization process but also a portion of severe manualhandling (bending, buckling and kinking), the retained strength is alsoreferred to as the ability to handle resistance or “handleability”.

Handleability Retained Strength Test Procedure

Cords are embedded between two layers of DUNLOP 5320 NR rubber compoundof 1-2 mm thickness in a form of 440 mm length, 190 mm width. Thelongitudinal cord layer (pitch 10 ends per inch (2.54 cm)) is maintainedin the central position. while the composite is preformed and vulcanizedin a mold at 160° C. during 20 to 30 min. After cooling, the obtainedslab is divided into straps of 1-inch (2.54 cm) width. From each strap,individual cord amples are extracted by hand. While one end of the strapis clamped in a vice, incisions between the cords are made at the otherend of the strap. The cords are then separated by being torn at anangle >90° away from the strap. The retained tensile strength of atleast six extracted cords is measured (omitting the outer cords of eachstrap).

Handle Perc. Ret. Strength

Handleability percentage retained strength=percentage of retainedstrength after vulcanization and manual handling relative to theabsolute breaking strength of the dip treated cord.$\frac{\begin{matrix}{{{Absolute}\quad{retained}\quad{strength}\quad{after}\quad{vulcanization}}\quad} \\{{and}\quad{manual}\quad{handling}\quad(N)}\end{matrix}}{\text{Absolute}\quad{breaking}\quad{strength}\quad{of}\quad{dipped}\quad{cord}\quad(N)} \times 100\quad(\%)$

TABLE 1 Tensile properties of Twaron 2300 development constructions.Cord construction Twaron 2300 1680 x2 Z190 x3 S115 Dip treatment stiffdipping soft dipped recipe pre-dip MDI (2.5%) MDI (5%) MDI (10%) T03(5%) T03 (1%) T03 (2%) Dip conditions recipe RFL dip A11 (20%) A11 (20%)A11 (20%) A11 (25%) A11 (25%) A11 (25%) Cord sample a b c d e f g h iDescription unit {overscore (X)} {overscore (X)} {overscore (X)}{overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)}{overscore (X)} {overscore (X)} Breaking strength N 1615 1643 1650 20612000 2003 1978 1796 1885 Elongation at break % 3.8 3.8 3.7 4.3 4.2 4.24.2 4.0 4.1 Force at specified N 372 381 392 398 389 393 397 380 397elongation 1% Force at specified N 779 801 827 876 850 868 868 820 842elongation 2% Force at specified N 1239 1269 1301 1379 1350 1375 13671307 1331 elongation 3% Dip efficieny % 78.8 80.1 80.4 96.8 93.1 94.092.3 84.2 88.5 absolute Strap peel force CR compound N/2 cm — — — 194235 189 235 — — Strap peel force NR compound N/2 cm — — — 222 294 221287 247 270 Handle.ret strength N 1390 1250 1120 1866 1880 1890 1850 — —Handle.perc.ret % 86.1 76.1 67.9 90.5 94.0 94.4 93.5 — — strength

EXAMPLE 3

Cord Constructions of Two-step Twisting (BISFA notations)

A: ((TWARON 2300 1680 dtex×2+PA6 44 dtex)×1 Z190+(2×(TWARON 2300 1680dtex×2 Z190)))S115.

The schematic view of Example 3A is shown in FIG. 5.

B: B: (2×(TWARON 2300 1680 dtex×2+PA6 44 dtex)×1 Z190)+TWARON 2300 1680dtex×2 Z190)S115.

The schematic view of Example 3B is shown in FIG. 6.

C: (TWARON 2300 1680 dtex×2+PA6 44 dtex)×1 Z190×S115.

The schematic view of Example 3C is shown in FIG. 7.

EXAMPLE 4

Cord Constructions of Three-steps Twisting (BISFA notations)

D: ((TWARON 2300 1680 dtex+PA6 44 dtex)+TWARON 2300 1680 dtexZ60)Z130+(2x(TWARON 2300 1680 dtex Z60×2 Z130))S115;

The schematic view of Example 4D is shown in FIG. 8.

E: (TWARON 2300 1680 dtex+PA6 44 dtex)Z60+TWARON 2300 1680dtexZ60)Z130×3 S115;

The schematic view of Example 4E is shown in FIG. 9.

F: (TWARON 2300 1680 dtex ×2+PA6 44 dtex)Z60×2 Z130×3 S115.

The schematic view of Example 4F is shown in FIG. 3.

1. A transmission belt comprising a cord, a rubber or thermoplasticmatrix, and an adhesion material able to adhere the cord to the rubberor thermoplastic matrix, wherein the cord comprises at least two yarns,a first yarn having a melting or decomposition point T₁ and a secondyarn having a melting point T₂, wherein T₁>T₂ and a ratio of a lineardensity of the first yarn to a linear density of the second yarn isbetween 1,000:1 and 1:1, and wherein the second yarn is fused to thefirst yarn.
 2. The transmission belt of claim 1, wherein the first yarnis an aramid or polyester yarn.
 3. The transmission belt of claim 1,wherein the rubber or thermoplastic matrix is a rubber matrix and theadhesion material is a resorcinol/formaldehyde/latex system.
 4. A methodof manufacturing a cord comprised of at least two yarns, a first yarnhaving a melting or decomposition point T₁ and a second yarn having amelting point T₂, wherein T₁>T₂ and a ratio of a linear density of thefirst yarn to a linear density of the second yarn is between 1,000:1 and1:1, and wherein the second yarn is fused to the first yarn, comprising:intertwining the first and the second yarn; heating the intertwinedfirst and second yarn to a temperature between T₁ and T₂; and dippingwith an adhesion material able to adhere the cord to a rubber orthermoplastic matrix, wherein the heating is conducted before or duringthe dipping.
 5. A method of manufacturing a transmission belt comprisingadhering the cord obtained by the method of claim 4 to a rubber orthermoplastic matrix.
 6. The transmission belt according to claim 1,wherein the ratio of a linear density of the first yarn to a lineardensity of the second yarn is between 100:1 and 4:1.
 7. The transmissionbelt according to claim 1, wherein the ratio of a linear density of thefirst yarn to a linear density of the second yarn is between 35:1 and15:1.
 8. The transmission belt according to claim 1, wherein the rubberor thermoplastic matrix is selected from the group consisting ofchloroprene rubber (CR), hydrogenated butadiene acrylonitrile rubber(HNBR), alkylated chlorosulfonated polyethylene (ACSM), ethylenepropylenediene rubber (EPDM) and polyurethane (PU).
 9. The transmissionbelt according to claim 1, wherein the adhesion material is selectedfrom the group consisting of epoxy compounds, polymeric methyl diphenyldiisocyanate and polyurethanes having ionic groups.
 10. The transmissionbelt according to claim 1, wherein the second yarn is selected from thegroup consisting of polyesters, polyamides, polyolefins, elastodienes,elastanes, thermoplastic vulcanizates, chlorofibers, cellulose, acetate,acrylic material and vinylal.
 11. The transmission belt according toclaim 1, wherein the first yarn and the second yarn are intertwined. 12.The method of manufacturing a cord according to claim 4, wherein theheating is integrated with the dipping.
 13. The method of manufacturinga cord according to claim 4, wherein the heating is performed before thedipping.
 14. The method of manufacturing a cord according to claim 4,wherein the ratio of a linear density of the first yarn to a lineardensity of the second yarn is between 100:1 and 4:1.
 15. The method ofmanufacturing a cord according to claim 4, wherein the ratio of a lineardensity of the first yarn to a linear density of the second yarn isbetween 35:1 and 15:1.
 16. The method of manufacturing a cord accordingto claim 4, wherein the intertwining of the first yarn and the secondyarn is performed as a three-step twisting scheme.
 17. The method ofmanufacturing a cord according to claim 4, wherein the intertwining ofthe first yarn and the second yarn is performed as a two-step twistingscheme.